color-for-external-cg-symbols

Returns the color that is used by colorize-source-code for symbols that are
external in the cg and ide packages, or nil
to avoid colorizing these symbols at all. This color may be useful
for warning when you have mistyped a Common Graphics symbol, or to
remind you that a particular function is a Common Graphics function
rather than one of your own.

The colorization is based only on the symbol's package and external
status, and will occur even where the symbol is not being used as the
function or variable for which it is exported.